The present invention generally relates to firearms, and more particularly to a handguard attachment or mounting system and related method for screw-in type firearm barrels.
In contrast to semi-automatic firearms such as AR-15 style rifles which have an action (i.e. operating system) that automatically cycles the bolt when the firearm is discharged to eject the spent ammunition shell and chamber a new shell, the bolt in a bolt action rifles must typically be cycled manually using a bolt handle to achieve the same result. Many modern bolt action stock and chassis systems have tubular hand-guards surrounding the barrel. This offers several benefits including flexible mounting options for lights, lasers or night vision devices, protection from unwanted contact with the free floated barrel and improved shielding of the hot barrel to reduce the mirage effect which may interfere with sighting the rifle. The majority of these handguards attaches directly to the chassis or stock, and in some cases are attached to the receiver. In most cases the main stock or chassis is positioned below the receiver, so the transition to the round handguard interface requires additional material or parts adding cost, weight and complexity.
One popular method of securing a “screw-in” threaded barrel to a receiver of the bolt action rifle is with a jam nut threaded onto the barrel that is tightened against the receiver when the barrel is in the correct location (see, e.g. FIG. 1). This effectively holds all of the components in place and allows a tight headspace dimensions to be held without requiring each barrel to be precisely machined to match a particular receiver and bolt. The externally threaded barrel is first threaded into a corresponding threaded bore in the front of the receiver, and then the jam nut is tightened to prevent the barrel to receiver interface from loosening when firing the rifle. This arrangement requires mounting free floating type tubular handguards to the chassis, receiver, or stock which has drawbacks as described above.
The barrel to receiver interface is achieved in a different manner in a semi-automatic AR-15 type rifle which supports mounting a free floating AR-15 type handguard. Such firearms utilize a slide-in type barrel arrangement. The aluminum upper receiver of an AR-15 type rifle has a forward projecting externally threaded portion or nipple that surrounds a plain bore sized to accept the barrel (see, e.g. FIG. 2). There is an external flange on the barrel extension threadably coupled to the rear of the barrel that sits just outside the receiver's externally thread portion that is positioned to contact an internal flange on an AR-15 style barrel nut when it is threaded onto upper receiver. There is a plurality of radially extending castellations on the barrel nut for conveniently clamping the tubular free floating handguard thereto in a simple manner without requiring additional parts or material.
Unlike the bolt action rifle barrel assembly shown in FIG. 1, the AR-15 barrel nut in FIG. 2 is not a jam nut. It secures the barrel assembly to the receiver by just forcing the flange on the barrel extension into contact with the upper receiver. The AR-15 barrel assembly is pre-headspaced so precise positioning during assembly is not required. A pin protruding from the barrel assembly engages the upper receiver to prevent relative rotation. The AR-15 barrel nut usually is applied with a torque between 35 and 80 ft-lbs (foot pounds).
Accordingly, an improved system which allows attachment of a free floating AR-15 type handguard to a bolt action rifle with screw-in barrel is desired.